The present invention relates to a rotation angle detecting apparatus for detecting a rotation angle and a surveying instrument for measuring an angle and a distance of an object to be measured.
A total station has become widespread as a surveying instrument for measuring an angle and a distance of an object to be measured in the civil engineering or construction field. The total station can highly accurately measure an angle and a distance of the object to be measured at from a short-distance to a long-distance, but an inexpensive and small total station with good mobility that is used at a site targeting a relatively short distance, e.g., the interior field etc. (which will be referred to as a mini total station hereinafter) has been recently demanded more.
As one of causes of an increase in price of the total station, there is a demand for high accuracy of an angle detection accuracy and a rotation accuracy.
An error of a measurement value due to an angular error is proportionate to a distance to a object to be measured, and hence an angular accuracy is demanded to a degree of a second. Therefore, a detection error of a rotation angle detecting apparatus and a rotation error (a tilt error involved by rotation on the rotational center) due to wobbling of a rotation shaft of a telescope for measurement which can be a cause of an angular error are strictly limited.
As a rotation angle detecting apparatus for use in a surveying instrument, an encoder has been conventionally adopted, and a highly accurate encoder is expensive. Further, it is difficult to set a rotation accuracy of a rotation shaft to a demanded accuracy, just by managing a processing accuracy of a lone component, and fine adjustment and fine finishing in an assembling state of the rotation shaft and a bearing holder are required, which results in expensiveness.